1. Field of the Invention
The present invention relates to apparatus for holding a cutting bit used to cut earth, rock, pavement and the like and, in particular, to an improved unitary cutting bit holding apparatus.
2. Description of the Invention Background
In the materials field mining and in other fields in which a large volume of hard materials must be cut, it is typical to employ an apparatus which includes a vertically moveable horizontal axis cutting drum having cutting bits attached thereto. By virtue of the engagement of the cutting bits which are mounted on the rotating cutting drum with the surface to be cut, material is removed from such surface for further processing.
Due to the substantial forces generated during the cutting operations, the cutting bits must be securely mounted on the cutting drums, but must also be readily removable for replacement. In one prior art form of cutting bit holding apparatus, a cutting bit having an elongated cylindrical shank and a hard cutting tip at one end and an abutment surface at the other end is retained in a bit holder which is usually welded to the cutting drum. Such bit holder includes a body portion having a forward surface (as taken in the cutting direction) and a rearward surface. A shank receiving bore extends through the body and forms openings in the forward and rearward surfaces for passage of the shank of the cutting bit therethrough.
The bit holder has a rearward extension terminating in a free-standing anvil portion having an anvil surface. The rearward end of the cutter bit shank extends beyond the rear surface of the bit holder body portion. The abutment surface on the cutting bit is adapted to cooperate with the anvil surface on the anvil portion so as to determine the depth to which the cutting bit extends into the shank receiving bore and to limit its axial movement during cutting operations. In addition, a retaining ring is provided about the rearward portion of the cutting bit shank to prevent forward axial removal of the cutting bit.
However, Applicant has discovered serious shortcomings with the above-described cutting bit holder. For example, due to the forces imparted on the bit holder by the cutting bit during the cutting operation, such prior art bit holders have catastrophically failed at the juncture of the rearward extension portion and the body portion of the bit holder. Also, such prior art bit holders have catastrophically failed in the body portion thereof by separating longitudinally along the shank receiving bore.
As will be appreciated, such failures of bit holders are quite costly because the cutting apparatus must be removed from service in order that the remaining portion of the bit holder may be cut away from the cutting drum and a replacement bit holder accurately welded onto the cutting drum. In addition, when the body portion of the bit holder fails along the cutting bit receiving bore, the cutting bit is frequently lost and must also be replaced.
The subject invention is directed toward an improved cutting bit holder which overcomes, among others, the above-described problems with prior art bit holders and provides a bit holder which is must less prone to such catastrophic failures and the concomittant apparatus downtimes, while being capable of being manufactured at similar costs thereto.